The goal of this research is to examine the signaling events regulating meiotic progression in mammalian oocytes. Immature oocytes are arrested at prophase I, and in response to a surge of luteinizing hormone LH) that acts on the follicle cells, they re-enter meiosis and mature into eggs. The mechanism(s) by which LH transmits its signal from the follicle cells to the oocyte is not known. Aim 1 of this proposal will examine signaling mechanisms by which LH initiates meiotic resumption in mouse oocytes. Prior to the LH surge, meiotic arrest requires a high level of cAMP in the oocyte;this cAMP is produced by the G-protein coupled receptor GPRS, in the oocyte plasma membrane, that stimulates Gs to activate adenylate cyclase. In response to LH, cAMP levels in the oocyte fall, leading to meiotic resumption. Potential targets in the oocyte by which LH could act include the following: 1) GPR3, which could be turned off through the activation of G- protein receptor kinases (GRKs) and li-arrestins, a common mechanism for downregulating most GPCRs. 2) Gs, the activity of which could be inhibited by a regulator of G-protein signalling (RGS) protein. 3) The AKT/PKB signalling pathway, which has been shown to affect meiotic resumption in a variety of species. 4) Regulation at the level of gap junctions. These pathways will be investigated using recently developed methods for microinjecting follicle-enclosed oocytes. Aim 2 will examine if meiotic arrest and resumption in human oocytes depend on the same pathways as in rodent oocyte, by examining if human oocytes contain the same components of these signalling pathways. Aim 2 will also characterize cytoplasmic events that normally occur during human oocyte maturation. These studies will provide valuable information about which aspects of rodent models can be applied to human oocytes. The question of how meiosis is regulated is highly relevant to issues of women's health. In particular, it is of high interest clinically to develop methods for successfully maturing immature human oocytes in vitro, which could lead to improvements in in vitro fertilization treatments, as well as provide more options than are currently available for women to preserve their fertility. Improvements in in vitro maturation will require an understanding of all stages of meiotic arrest and the physiological mechanisms regulating the initiation of oocyte maturation. The proposed studies will contribute to the basic science background that underlies such clinical advances.